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通过服务器中转消息，实现多客户端之间的对话。客户端输入格式为：接受消息的客户端编号+空格+要发出的消息。客户端输入end下线。有客户端上线或下线，服务器都会通知其他客户端情况。效果如下图：
1.服务端
服务端为连接上的每一个客户端，提供一个接受线程，监听接受消息，在向客户端发送消息时会临时开启一个发送线程。
import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;
/**
* Created by HeTingwei on 2017/12/9.
* 多线程服务器,实现多客户端聊天
*/
public class Server {
List<ReceiveThread> receiveList = new ArrayList<>();//存放已连接客户端类
private final static int MESSAGE_SIZE = 1024;//每次允许接受数据的最大长度
int num = 0;//客户端编号
public static void main(String[] args) {
new Server();
}
//服务端处理逻辑
Server() {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(45678);//用来监听的套接字，指定端口号
while (true) {
Socket socket = serverSocket.accept();//监听客户端连接，阻塞线程
System.out.println("连接上客户端：" + num);
//在其他线程处理接收来自客户端的消息
ReceiveThread receiveThread = new ReceiveThread(socket, num);
receiveThread.start();
receiveList.add(receiveThread);
//有客户端新上线，服务器就通知其他客户端
String notice="有新客户端上线，现在在线客户端有：客户端:";
for (ReceiveThread thread : receiveList) {
notice = notice + "" + thread.num;
}
for (ReceiveThread thread : receiveList) {
new SendThread(thread.socket, notice).start();
}
num++;
}
} catch (IOException e) {
e.printStackTrace();
}
}
//接受消息的线程（同时也有记录对应客户端socket的作用）
class ReceiveThread extends Thread {
int num;
Socket socket;//客户端对应的套接字
boolean continueReceive = true;//标识是否还维持连接需要接收
public ReceiveThread(Socket socket, int num) {
this.socket = socket;
this.num = num;
try {
//给连接上的客户端发送，分配的客户端编号的通知
socket.getOutputStream().write(("你的客户端编号是" + num).getBytes());
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public void run() {
super.run();
//接收客户端发送的消息
InputStream inputStream = null;
try {
inputStream = socket.getInputStream();
byte[] b;
while (continueReceive) {
b = new byte[MESSAGE_SIZE];
inputStream.read(b);
b = splitByte(b);//去掉数组无用部分
//发送end的客户端断开连接
if (new String(b).equals("end")) {
continueReceive = false;
receiveList.remove(this);
//通知其他客户端
String message = "客户端" + num + "连接断开\n" +
"现在在线的有，客户端：";
for (ReceiveThread receiveThread : receiveList) {
message = message + " " + receiveThread.num;
}
System.out.println(message);
for (ReceiveThread receiveThread : receiveList) {
new SendThread(receiveThread.socket, message).start();
}
} else {
try {
String[] data = new String(b).split(" ", 2);//以第一个空格，将字符串分成两个部分
int clientNum = Integer.parseInt(data[0]);//转换为数字，即客户端编号数字
//将消息发送给指定客户端
for (ReceiveThread receiveThread : receiveList) {
if (receiveThread.num == clientNum) {
new SendThread(receiveThread.socket, "客户端"+num+"发消息："+data[1]).start();
System.out.println("客户端" + num + "发送消息到客户端" + receiveThread.num + ": " + data[1]);
}
}
} catch (Exception e) {
new SendThread(socket, "输入错误，请重新输入").start();
System.out.println("客户端输入错误");
}
}
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {//关闭资源
if (inputStream != null) {
inputStream.close();
}
if (socket != null) {
socket.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
//发送消息的线程
class SendThread extends Thread {
Socket socket;
String str;
public SendThread(Socket socket, String str) {
this.socket = socket;
this.str = str;
}
@Override
public void run() {
super.run();
try {
socket.getOutputStream().write(str.getBytes());
} catch (IOException e) {
e.printStackTrace();
}
}
}
//去除byte数组多余部分
private byte[] splitByte(byte b[]) {
int i = 0;
for(;i<b.length;i++) {
if (b[i] == 0) {
break;
}
}
byte[] b2 = new byte[i];
for (int j = 0; j <i ; j++) {
b2[j] = b[j];
}
return b2;
}
}
2.客户端
在主线程中接受键盘输入，并发送消息，在子线程中接受消息。
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;
import java.util.Scanner;
/**
* Created by HeTingwei on 2017/12/9.
* 多线程客户端
*/
public class Client {
Socket socket;
private static final int MESSAGE_SIZE = 1024;//每次允许接受数据的最大长度
public static void main(String[] args) {
new Client();
}
public Client() {
try {
socket = new Socket("127.0.0.1", 45678);
if (socket.isConnected() == true) {
System.out.println("连接成功");
new Thread() {//开启一个接受数据的线程
@Override
public void run() {
super.run();
InputStream in;
try {
in = socket.getInputStream();
byte[] b;
while (true) {
b = new byte[MESSAGE_SIZE];
in.read(b);
System.out.println("接收到服务端消息：" + new String(b));
}
} catch (IOException e) {
e.printStackTrace();
}
}
}.start();
}
OutputStream out = null;
while (true) {
Scanner scanner = new Scanner(System.in);
String str = scanner.nextLine();
out = socket.getOutputStream();
out.write(str.getBytes());
out.flush();
if (str.equals("end")) {
System.exit(0);//关闭客户端
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}